Method for changing aid in wireless LAN system

ABSTRACT

Disclosed is a method for changing an AID in a wireless LAN system. The method for changing an AID of a terminal by an access point comprises: a step of receiving an AID reassignment frame from the access point; a step of extracting an AID reassignment counter value from the AID reassignment frame; and a step of changing the AID of the terminal to the new AID included in the AID reassignment frame after the beacon periods of the access point indicated by the AID reassignment counter value extracted from the AID reassignment frame reception time have elapsed. Thus, a conflict between AIDs can be prevented.

CLAIM FOR PRIORITY

This application claims priority to Korean Patent Application No.2012-0069963 filed on Jun. 28, 2012, No. 2013-0035516 filed on Apr. 2,2013 and No. 2013-0054185 filed on May 14, 2013 in the KoreanIntellectual Property Office (KIPO), the entire contents of which arehereby incorporated by reference.

BACKGROUND

1. Technical Field

Example embodiments of the present invention relate in general to amethod of changing an association ID (AID) and more specifically to amethod of changing an old AID to a new AID in a wireless local areanetwork (WLAN) system.

2. Related Art

Various wireless communication techniques are being developed along withthe recent development of an information communication technology. Inparticular, wireless local area network (WLAN) is a technology that canprovide a wireless connection to the Internet in a limited service areasuch as a home or office building using portable terminals, for example,a personal digital assistant (PDA), a laptop computer, and a portablemultimedia player (PMP) based on a wireless frequency technology.

Standards for WLAN technology is developed and standardized by IEEE802.11 working group (WG) in the Institute of Electrical and ElectronicsEngineering (IEEE) 802.11. IEEE 802.11a provides a transfer rate of 54Mbps using 5 GHz unlicensed band. IEEE 802.11b provides a transfer rateof 11 Mbps by using direct sequence spread spectrum (DSSS) in 2.4 GHzband. IEEE 802.11g provides a transfer rate of 54 Mbps by usingorthogonal frequency division multiplexing (OFDM) in 2.4 GHz band. IEEE802.11n provides a transfer rate of 300 Mbps for two spatial streams byusing multiple-input multiple-output OFDM (MIMO-OFDM). IEEE 802.11nsupports a channel bandwidth of up to 40 MHz and, in this case, providesa transfer rate of 600 Mbps.

Along with the wide deployment of WLAN and the diversification ofapplications using WLAN, new WLAN techniques are increasingly needed tosupport higher throughput than IEEE 802.11n. Very high throughput (VHT)WLAN is one of IEEE 802.11 WLAN techniques, which is proposed to supporta data processing rate of 1 Gbps or more. In particular, IEEE 802.11acis developed as a standard for providing a very high throughput on the 5GHz band, and IEEE 802.11ad is developed as a standard for providing avery high throughput on the 60 GHz band.

In systems based on the WLAN techniques, an access point (AP) managesstations by assigning a unique association ID (AID) to each of thestations whenever the station accesses the AP. During an operationbetween the AP and the station in the WLAN system, the AID, which is aunique number of the station, may be needed to be changed. Whenreassigning an AID to the station, the AP may reassign a new AID to thestation, and the station may change an old AID to the reassigned newAID. In this case, when AIDs are reassigned to a plurality of stations,times at which old AIDs are changed to the reassigned new AIDs may bedifferent for each station, resulting in a collision between the AIDs.

SUMMARY

Accordingly, example embodiments of the present invention are providedto substantially obviate one or more problems due to limitations anddisadvantages of the related art.

Example embodiments of the present invention provide a method ofchanging an AID of a station, which may prevent a collision between AIDswhen an AID is changed in a WLAN system.

In some example embodiments, a method of changing an association ID(AID) of a terminal includes receiving an AID reassignment frame from anaccess point; extracting an AID reassignment counter value from the AIDreassignment frame; and changing the AID of the terminal to a new AIDincluded in the AID reassignment frame after beacon intervals of theaccess point that are indicated by the extracted AID reassignmentcounter value have passed since a reception time of the AID reassignmentframe.

When the AID reassignment counter value extracted in the extracting ofthe AID reassignment counter value is zero, the changing of the AID ofthe terminal may include changing the AID of the terminal to the new AIDincluded in the AID reassignment frame at the reception time of the AIDreassignment frame.

The AID reassignment frame may be received corresponding to a power save(PS)-Poll frame transmitted by the terminal to the access point.

When there is at least one terminal having an AID that is to be changedsimultaneously with the AID of the terminal, the AID reassignmentcounter value may be determined in consideration of both of a listeninterval of the terminal and a listen interval of the at least oneterminal.

The AID reassignment counter value may be configured such that the AIDof the terminal is changed after a longest listen interval among thelisten interval of the terminal and the listen interval of the at leastone terminal.

In other example embodiments, a method of reassigning, by an accesspoint, an association ID (AID) of a terminal may include generating anAID reassignment frame including an AID reassignment counter value thatdesignates a new AID and a time at which a change to the new AID ismade; and transmitting the AID reassignment frame to the terminal,wherein the AID reassignment counter value indicates that the AID of theterminal is changed to a new AID included in the AID reassignment frameafter beacon intervals of the access point that are indicated by the AIDreassignment counter value have passed since a transmission time of theAID reassignment frame.

When the AID reassignment counter value is zero, the AID reassignmentcounter value indicates that the AID of the terminal is changed to thenew AID at the transmission time of the AID reassignment frame.

The AID reassignment frame may be received corresponding to a power save(PS)-Poll frame received by the access point from the terminal.

When there is at least one terminal having an AID that is to be changedsimultaneously with the AID of the terminal, the AID reassignmentcounter value may be determined in consideration of both of a listeninterval of the terminal and a listen interval of the at least oneterminal.

The AID reassignment counter value may be configured such that the AIDof the terminal is changed after a longest listen interval among thelisten interval of the terminal and the listen interval of the at leastone terminal.

BRIEF DESCRIPTION OF DRAWINGS

Example embodiments of the present invention will become more apparentby describing in detail example embodiments of the present inventionwith reference to the accompanying drawings, in which:

FIG. 1 is a conceptual view showing a configuration of an IEEE 802.11WLAN system according to an embodiment of the present invention;

FIG. 2 is a conceptual view showing an association process for aterminal in an infrastructure BSS;

FIG. 3 is a block diagram showing an element of a traffic indication map(TIM) included in a beacon according to an embodiment of the presentinvention;

FIG. 4 is a conceptual view showing a data transmission process for anaccess point according to an embodiment of the present invention;

FIG. 5 is a block diagram showing a frame structure for designating aservice type of a terminal according to an embodiment of the presentinvention;

FIG. 6 is a block diagram showing an AID structure according to anembodiment of the present invention;

FIG. 7 is a conceptual view showing a structure of a TIM that is encodedin units of blocks according to an embodiment of the present invention;

FIG. 8 is a conceptual view showing a process of reassigning an AID to agroup;

FIG. 9 is a flowchart showing an AID change method according to anembodiment of the present invention;

FIG. 10 is a block diagram showing an AID reassignment frame accordingto an embodiment of the present invention; and

FIG. 11 is a conceptual view showing an AID change process for aplurality of stations.

DESCRIPTION OF EXAMPLE EMBODIMENTS

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail.

However, it is to be understood that the present invention is notlimited to the specific exemplary embodiments, but includes allmodifications, equivalents, and substitutions included in the spirit andthe scope of the present invention.

Relational terms such as first, second, and the like may be used fordescribing various elements, but the elements should not be limited bythe terms. These terms are only used to distinguish one element fromanother. For example, a first component may be named a second componentwithout being departed from the scope of the present invention and thesecond component may also be similarly named the first component. Theuse of the term of ‘and/or’ means that combination of a plurality ofrelated and described items or one items among a plurality of relatedand described items is included.

When it is mentioned that a certain component is “coupled with” or“connected with” another component, it may be understood that anothercomponent can exist between the two components although the componentcan be directly coupled or connected with the another component.Meanwhile, when it is mentioned that a certain component is “directlycoupled with” or “directly connected with” another component, it has tobe understood that another component does not exist between the twocomponents.

In the following description, the technical terms are used only forexplaining a specific exemplary embodiment while not limiting thepresent disclosure. Singular forms used herein are intended to includeplural forms unless explicitly indicated otherwise. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes,” and/or“including” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or a combinationthereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. Terms suchas terms that are generally used and have been in dictionaries should beconstrued as having meanings matched with contextual meanings in theart. In this description, unless defined clearly, terms are not ideally,excessively construed as formal meanings.

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Indescribing the invention, in order to facilitate the overallunderstanding of the invention, like numbers refer to like elementsthroughout the description of the figures and the repetitive descriptionthereof will be omitted.

Throughout this specification, a station (hereinafter also referred toas an STA) is any functional medium including a medium access control(MAC) and wireless-medium physical layer (PHY) interface conforming tothe IEEE 802.11 standard. The STA may include an access point (AS) STAand a non-AP STA. The AP STA may be simply referred to as an accesspoint (hereinafter also referred to as an AP), and the non-AP STA issimply referred to as a terminal.

The STA includes a processor and a transceiver, and may further includea user interface, a display device, and so on. The processor is afunctional unit devised to generate a frame to be transmitted through awireless network or to process a frame received through the wirelessnetwork, and performs various functions to control the STA. Thetransceiver is functionally connected to the processor and is afunctional unit devised to transmit and receive a frame for the STAthrough the wireless network.

The AP may be called a convergence controller, a base station (BS), anode-B, an eNode-B, a base transceiver system, or a site controller, andmay include some or all of functions thereof.

The terminal may be called a wireless transmit/receive unit (WTRU), auser equipment (UE), a user terminal (UT), an access terminal (AT), amobile station (MS), a mobile terminal, a subscriber unit, a subscriberstation (SS), a wireless device, a mobile subscriber unit, or the likeand may include some or all of functions thereof.

Here, the terminal may include a communication enabled desktop computer,laptop computer, tablet PC, wireless phone, mobile phone, smartphone,e-book reader, portable multimedia player (PMP), portable gamingconsole, navigation device, digital camera, digital multimediabroadcasting (DMB) player, digital audio recorder, digital audio player,digital picture recorder, digital picture player, digital videorecorder, digital video player, etc.

FIG. 1 is a conceptual view showing a configuration of an IEEE 802.11WLAN system according to an embodiment of the present invention.

Referring to FIG. 1, the IEEE 802.11 WLAN system includes at least onebasic service set (BSS). The BBS denotes a set of stations STA 1, STA 2(AP 1 ), STA 3, STA 4, and STA 5 (AP 2 ) that may be successfullysynchronized to communicate with one another, but does not denote acertain region.

The BBS may be classified into an infrastructure BSS and an independentBSS (IBSS). BBS 1 and BBS 1 denote the infrastructure BSS. BBS 1 mayinclude a terminal STA 1, an access point STA 2 (AP 1 ) that provides adistribution service, and a distribution system (DS) that connects aplurality of access points STA 2 (AP 1 ) and STA 5 (AP 2 ). In BSS 1,the access point STA 2 (AP 1 ) manages the terminal STA 1.

BBS 1 may include the terminals STA 3 and STA 4, the access point STA 5(AP 2 ) that provides a distribution service, and a distribution systemthat connects the plurality of access points STA 2 (AP 1 ) and STA 5 (AP2 ). In BSS 2, the access point STA 5 (AP 2 ) manages the terminals STA3 and STA 4.

The independent BSS (IBSS) is a BSS that operates in an ad-hoc mode.Since the IBSS does not include an access point, there is no centralizedmanagement entity for performing a central management function. That is,in the IBSS, terminals are managed in a distributed manner. The IBSS isa self-contained network, in which all terminals may be mobile terminalsand may be disallowed to access the distribution system (DS).

The access points STA 2 (AP 1 ) and STA 5 (AP 2 ) provide a connectionto the DS through a wireless medium for the associated terminals STA 1,STA 3, and STA 4. In BSS 1 or BSS 2, generally, a communication betweenthe terminals STA 1, STA 3, and STA 4 is made through the access pointsSTA 2 (AP 1 ) and STA 5 (AP 2 ). However, when a direct link isestablished, a direct communication between the terminals STA 1, STA 3,and STA 4 is enabled.

A plurality of infrastructure BBSs may be interconnected through the DS.The plurality of BBSs connected to each other through the DS is calledan extended service set (ESS). STAs included in the ESS may communicatewith each other, and within the same ESS, a terminal may move from oneBSS to another BSS while communicating in a seamless manner.

The DS is a mechanism in which one AP communicates with another AP. Byusing the DS, an AP may transmit a frame to terminals that is associatedwith a BSS managed by the AP, or transmit a frame to a terminal that hasmoved to another BSS. In addition, the AP may transmit and receive aframe to and from an external network such as a wired network. The DS isnot necessarily a network and has no limitation in its form as long as apredetermined distribution service specified in the IEEE 802.11 standardcan be provided. For example, the DS may be a wireless network such as amesh network, or may be a physical structure for interconnecting APs.

An AID change method according to an embodiment of the presentinvention, which will be described below, may be applied to the aboveIEEE 802.11 WLAN system and also various networks such as a wirelesspersonal area network (WPAN), a wireless body area network (WBAN), andso on.

FIG. 2 is a conceptual view showing an association process for aterminal in an infrastructure BSS.

In order for a terminal STA to transmit and receive data in aninfrastructure BSS, first, the terminal STA should be associated with anAP.

Referring to FIG. 2, the association process of the terminal STA in theinfrastructure BSS may include: 1) probe step of probing an AP, 2)authentication step of authenticating the probed AP, and 3) associationstep of associating with the authenticated AP.

First, the terminal STA may probe neighboring APs through the probeprocess. The probe process includes a passive scanning method and anactive scanning method. The passive scanning method may be performed byoverhearing beacons that are transmitted by the neighboring APs. On theother hand, the active scanning method may be performed by broadcastinga probe request frame. Upon receiving the probe request frame, the APmay transmit a probe response frame corresponding to the probe requestframe to the terminal STA. The terminal STA may check the presence ofthe neighboring APs by receiving the probe response frame.

Subsequently, the terminal STA performs authentication with the probedAPs, and may perform the authentication with the plurality of APs. Anauthentication algorithm conforming to the IEEE 802.11 standard includesan open system algorithm that exchanges two authentication frames and ashared key algorithm that exchanges four authentication frames. Througha process of exchanging the authentication request frame and theauthentication response frame based on the authentication algorithm, theterminal STA may perform authentication with the AP.

Last, the terminal STA selects one AP from among the authenticatedplurality of APs and performs an association process with the selectedAP. That is, the terminal STA transmits an association request frame tothe selected AP. Upon receiving the association request frame, the APtransmits the terminal STA to an association response framecorresponding to the association request frame. As such, through theprocess of exchanging the association request frame and the associationresponse frame, the terminal STA may perform the association processwith the AP.

FIG. 3 is a block diagram showing an element of a traffic indication map(TIM) included in a beacon according to an embodiment of the presentinvention.

In the IEEE 802.11 WLAN system, when there is data to be transmitted tothe terminal, the AP notifies the terminal that there is data to betransmitted using a TIM in a beacon frame that is periodicallytransmitted.

Referring to FIG. 3, the TIM includes an element ID field, a lengthfield, a delivery traffic indication message (DTIM) count field, a DTIMperiod field, a bitmap control field, and a partial virtual bitmapfield.

The length field indicates a length of an information field. The DTIMcount field indicates the number of beacons before the DTIM. When a DTIMcounter is 0, a current TIM is the DTIM. The DTIM counter field iscomposed of 1 octet. The DTIM period field indicates the number ofbeacon intervals between consecutive DTIMs. If all TIMs are the DTIMs, avalue of the DTIM period field is 1. The DTIM period field is composedof 1 octet.

The bitmap control field is composed of 1 octet, and a bit number 0 ofthe bitmap control field denotes a traffic indicator bit that isassociated with an association ID (AID) 0. When the bit is set as 1 andthe value of the DTIM counter field is 0, it can be seen that at leastone multicast or broadcast frame is buffered in the AP. The remaining 7bits of the bitmap control field form a bitmap offset.

The partial virtual bitmap field is composed of 1 to 251 octets, and abit number N has a value in a range of 0 to 2007. Each bit of thepartial virtual bitmap field corresponds to traffic that is buffered fora specific terminal. In a case in which an AID of any terminal is N, thebit number N of the partial virtual bitmap field is set as 0 when thereis no buffered traffic and the bit number N of the partial virtualbitmap field is set as 1 when there is buffered traffic.

FIG. 4 is a conceptual view showing a data transmission process for anaccess point according to an embodiment of the present invention.

Referring to FIG. 4, the AP broadcasts a beacon periodically and maybroadcast a beacon including the DTIM at every 3 beacon intervals. Theterminals STA 1 and STA2 periodically wake up from a power save mode(PSM) and receive the beacon, and check the TIM or DTIM included in thebeacon to determine whether the data to be transmitted to the terminalsis buffered in the AP. In this case, when there is the buffered data,the terminals STA 1 and STA 2 maintain awake and receive the data fromthe AP. When there is no buffered data, the terminals STA 1 and STA 2return to the PSM (that is, a doze state).

That is, when a bit in the TIM corresponding to an AID of the terminalSTA 1 or STA 2 is set as 1, the terminal STA 1 or STA 2 transmits, tothe AP, a power save (PS)-Poll frame (or a trigger frame) that informsthe AP that the terminal STA is awake and ready to receive data. The APmay determine that the terminal STA 1 or STA 2 is ready to receive thedata by receiving the PS-Poll frame and then may transmit the data or anacknowledgement (ACK) to the terminal STA 1 or STA 2. When the APtransmits the ACK to the terminal STA 1 or STA 2, the AP transmits datato the terminal STA 1 or STA 2 at an appropriate time. On the otherhand, when the bit in the TIM corresponding to the AID of the terminalSTA 1 or STA 2 is set as 0, the terminal STA 1 or STA 2 returns to thePSM.

A one-time bit setting for AIDs of a plurality of terminals may beenabled on the TIM (or DTIM) included in the beacon. Accordingly, afterthe AP broadcasts a beacon, a plurality of terminals, in which bitscorresponding to their own AIDs are set as 1, transmit the PS-Poll tothe AP at the same time. In this case, wireless channel accesscompetitions for transmitting the PS-Poll frame between the plurality ofterminals are getting worse, and in addition, collisions between theterminals may occur due to a hidden node problem, which is a chronicproblem in a WLAN system.

For example, the above described situations may frequently occur in aWLAN service that supports thousands of low-power sensor terminals. Inthis case, since the terminal s should keep awake to completely receivedata or repeatedly perform retransmission of the PS-Poll frame that isnot transmitted due to the collision, power consumption may be serious.

FIG. 6 is a block diagram showing an AID structure according to anembodiment of the present invention, and FIG. 5 is a block diagramshowing a frame structure for designating a service type of a terminalaccording to an embodiment of the present invention.

When there are many terminals that receive a service through one AP andthe terminals may be grouped by similar characteristics, the AP maygroup and manage AIDs of the terminals.

Referring to FIG. 6, the AID structure includes a page ID field, a blockindex field, a sub-block index field, and a STA bit index field. Thatis, the AID may be managed as a hierarchical group in units ofpages/blocks/sub-blocks.

Referring to FIG. 5, a terminal may designate a service type of anassociation request frame and transmit the service type to the AP. Theservice type may include a type of a low-power terminal, a type of aterminal having a channel access priority, a type of a general terminal,etc.

That is, the terminal may transmit the association request frame inwhich the service type is designated to the AP, and the AP may designatea group of the terminal using pages/blocks/sub-blocks corresponding tothe service type and assign an AID according to the designated group.

FIG. 7 is a conceptual view showing a structure of a TIM that is encodedin units of blocks according to an embodiment of the present invention.

Referring to FIG. 7, the partial virtual bitmap field includes at leastone block field (block L, block M, . . . , block P). One block fieldincludes a block control field, a block offset field, a block bitmapfield, and a sub-block field having various sizes. The sub-block fieldincludes at least one sub-block bitmap field (sub-block bitmap 1,sub-block bitmap 2, . . . , sub-block bitmap M).

The block control field indicates a TIM encoding mode (that is, a blockbitmap mode, a single AID mode, an OLB (offset+length+bitmap) mode, oran inverse mode). The block offset field indicates an offset value ofthe encoded block. The block bitmap field is a bitmap indicating asub-block in which an AID bit is set among sub-blocks in a block that isindicated by the block offset. The sub-block field indicates a bit mapfor the AID in the sub-block.

FIG. 8 is a conceptual view showing a process of reassigning an AID to agroup.

Referring to FIG. 8, when traffic having a specific period increases andthus a group including stations STA 1, STA 2, and STA 3 needs to bechanged while the AP groups and manages the stations STA 1, STA 2, andSTA 3, the AP may transmit an AID reassignment frame to a correspondingSTA after transmitting the DTIM or receiving the PS-Poll from the STA.

That is, the AP may manage the stations STA 1, STA 2, and STA 3 as onegroup, and the stations STA 1, STA 2, and STA 3 may have PID 1 as agroup ID. When traffic for group 1 including the stations STA 1, STA 2,and STA 3 increases, the AP may transmit an AID reassignment frame toSTA 2 and STA 3 in order to manage STA 2 and STA 3 as another group (forexample, group 2). Upon receiving the AID reassignment frame, STA 2 andSTA 3 may change their group ID from PID 1 to PID 2.

The AP may assign, to each station that requests an association, an AIDof a group corresponding to characteristics of the station and mayreceive and operate the same number of stations as the maximum number ofAIDs that can be assigned. As a result, when all AIDs are used, allgroup AID (that is, the number of AIDs is predetermined for loadbalancing for each group) are used, or an AID change is needed foranother reason, the AIDs of the plurality of stations should besimultaneously changed. However, since listen interval values of thestations are different from each other and also wake-up times of thestations are different from each other, the AIDs cannot be changedsimultaneously, thus causing AID collisions.

FIG. 9 is a flowchart showing a method of changing an AID according toan embodiment of the present invention.

Referring to FIG. 9, the AP 10 may broadcast a beacon including a TIM orDTIM (S100). Among STA 1 20 and STA 2 30, STA 1 20 may wake up from apower save mode (PSM) earlier than STA 2 30 and transmit a PS-Poll tothe AP 10 (S101).

Upon receiving the PS-Poll of STA 1 20, the AP 10 may generate an AIDreassignment frame (S102). That is, when the AP 10 desires to changeAIDs of STA 1 20 and STA 2 30, the AP 10 may generate the AIDreassignment frame upon receiving the PS-Poll from STA 1 20 or STA 2 30.

The AID reassignment frame may include a desired new AID and an AIDreassignment counter value that designates a time at which a change tothe new AID is made. The AID reassignment counter indicates a time atwhich an old AID is changed to a new AID (that is, a new AID included inthe AID reassignment frame) and denotes the number of beacon intervalsof the access point 10. For example, the AID reassignment counter valueof 5 indicates that the old AID is changed to the new AID after fivebeacon intervals have passed since a reception time of the AIDreassignment counter, and the AID reassignment counter value of 0indicates that the old AID is changed to the new AID when the AIDreassignment counter is received.

When the AP 10 desires to change the AIDs of STA 1 20 and STA 2 30 atthe same time, the AP 10 may set an AID reassignment counter value inconsideration of both of a listen interval of STA 1 20 and a listeninterval of STA 2 30. That is, the AP 10 may set the AID reassignmentcounter value such that an old AID is changed to a new AID after alongest listen interval among the listen interval of STA 1 20 and thelisten interval of STA 2 30

For example, at a current time, when the number of remaining listenintervals of STA 1 20 is 5 and the number of remaining listen intervalsof STA 2 30 is 10, the AP 10 may set the AID reassignment counter valuefor STA 1 20 and STA 2 30 as 10.

FIG. 10 is a block diagram showing an AID reassignment frame accordingto an embodiment of the present invention.

Referring to FIG. 10, a body of the AID reassignment frame may include acategory field, an action value field, and an AID reassignment elementfield. Here, the category field may have a size of 1 octet, and theaction value field may have a size of 1 octet.

The AID reassignment element field may have a size of 6 octets andinclude an element ID field, a length field, a new AID value field, andan AID reassignment counter field. The element ID field may have a sizeof 1 octet, and the length field may have a size of 1 octet. The new AIDvalue field may indicate an AID value intended to be changed and have asize of 2 octets. The AID reassignment counter field may indicate a timeat which an old AID is changed to a new AID and have a size of 2 octets.

Here, the AID reassignment frame is not limited to a frame that is shownin FIG. 10, and may include various forms.

Referring again to FIG. 9, the AP 10 may transmit an AID reassignmentframe to STA 1 20 (S103). The AP 10 may start an AID reassignmentcounter for an AP, which has the AID reassignment counter value includedin the AID reassignment frame as an initial value after transmitting theAID reassignment frame (or while transmitting the AID reassignmentframe) (S104). The AID reassignment counter for the AP is a counter usedinside the AP 10 that decreases by 1 whenever the beacon is transmittedand expires when the counter reaches zero. When the AID reassignmentcounter for the AP is zero, the AP 10 applies a new ID to acorresponding station.

Even when the AP 10 does not receive a PS-Poll from STA 1 20, the AP 10may generate the AID reassignment frame. That is, when the AP 10 sets aTIM bitmap corresponding to the AID of STA 1 20 to broadcast a beacon,the AP 10 may generate the AID reassignment frame and transmit the AIDreassignment frame to STA 1 20 after a predefined time (for example,SIFS etc.) has passed.

Alternatively, when the AP 10 receives a specific frame that requestsAID reassignment from STA 1 20, the AP 10 may generate the AIDreassignment frame and transmit the AID reassignment frame to STA 1 20after a predefined time (for example, SIFS etc.) has passed.

Here, upon receiving the AID reassignment frame, STA 1 20 may transmitan ACK frame, which is a response to the reception of the AIDreassignment frame, to the AP 10.

Upon receiving the AID reassignment frame, STA 1 20 may extract an AIDreassignment counter value from the AID reassignment frame (S105). Inthis case, when the extracted AID reassignment counter value is zero,STA 1 20 may change an old AID to a new AID (that is, a new AID includedin the AID reassignment frame).

On the other hand, when the extracted AID reassignment counter value isnot zero, STA 1 20 may start an AID reassignment counter for STA 1having the AID reassignment counter value as an initial value (S106).The AID reassignment counter for STA 1 is a counter that is used insideSTA 1 20, and STA 1 20 may decrease the AID reassignment counter by 1whenever receiving the beacon or decrease the AID reassignment counterby 1 at beacon intervals (for example, every 100 ms).

Then, the AP 10 may broadcast a beacon at beacon intervals (S107). Aftertransmitting the beacon (or while transmitting the beacon), the AP 10may decrease the AID reassignment counter by 1 (S108). STA 1 20 maydecrease the AID reassignment counter by 1 when the beacon is receivedor when the beacon interval has passed (S109).

STA 2 30 may wake up from a power save mode and transmit a PS-Poll tothe AP 10 (S110). Upon receiving the PS-Poll of STA 2 30, the AP 10 maytransmits the AID reassignment frame including the AID reassignmentcounter value at a current time to STA 2 30 (S111).

Upon receiving the AID reassignment frame, STA 2 30 may extract an AIDreassignment counter value from the AID reassignment frame (S112). Inthis case, when the extracted AID reassignment counter value is zero,STA 2 30 may change an old AID to a new AID (that is, a new AID includedin the AID reassignment frame).

On the other hand, when the extracted AID reassignment counter value isnot zero, STA 2 30 may start an AID reassignment counter for STA 2having the AID reassignment counter value as an initial value (S113).The AID reassignment counter for STA 2 is a counter that is used insideSTA 2 30, and STA 2 30 may decrease the AID reassignment counter by 1whenever receiving the beacon or decrease the AID reassignment counterby 1 at beacon intervals (for example, every 100 ms).

Then, the AP 10 may broadcast a beacon at beacon intervals (S114). TheAP 10 may decrease the AID reassignment counter by 1 after transmittingthe beacon (or while transmitting the beacon), and may apply a new AIDwhen the AID reassignment counter reaches zero (S115). The STA 1 20 maydecrease the AID reassignment counter by 1 when the beacon is receivedor the beacon interval has passed, and may change an old AID to a newAID when the AID reassignment counter reaches zero (S116). The STA 2 30may decrease the AID reassignment counter by 1 when the beacon isreceived or the beacon interval has passed, and may change an old AID toa new AID when the AID reassignment counter reaches zero (S117).

That is, the AID reassignment counter values of the AP 10 and thestations 20 and 30 are all zero when any beacon is transmitted (or atany beacon interval). At this point, the AP 10 may apply new AIDs to thestations 20 and 30, and the stations 20 and 30 may change old AIDs tothe new AIDs.

FIG. 11 is a conceptual view showing an AID change process for aplurality of stations.

Referring to FIG. 11, when the AIDs of STA 1 and STA 2 are intended tobe changed at the same time, the AP may generate an AID reassignmentframe. The AID reassignment frame may include a new AID and an AIDreassignment counter that indicates a time at which a change to the newAID is made.

When the AID of STA 1 is intended to be changed from 1000 to 2000, theAP may determine a new AID included in an AID reassignment frame for STA1 as 2000. When the AID of STA 2 is intended to be changed from 2000 to1000, the AP may determine a new AID included in an AID reassignmentframe for STA 2 as 1000.

When the AP determines the AID reassignment counter, the AP may considera listen interval of STA 1 and a listen interval of STA 2. In this case,the AP may determine a longest listen interval among the listen intervalof STA 1 and the listen interval of STA 2 as the AID reassignmentcounter. That is, since the number of listen intervals of STA 1 is 5 andthe number of listen intervals of STA 2 is 30, the AP may determine theAID reassignment counter included in the AID reassignment frames for STA1 and STA 2 as 30.

According to the above process, the AID reassignment frame for STA 1 hasthe new AID of 2000 and the AID reassignment counter of 30. The AIDreassignment frame for STA 2 has the new AID of 1000 and the AIDreassignment counter of 30.

STA 1 may wake up from a power save mode and transmit a PS-Poll to theAP 10. Upon receiving the PS-Poll from STA 1, the AP may generate theabove AID reassignment frame (new AID: 2000 and AID reassignmentcounter: 29) and transmit the generated AID reassignment frame to STA 1.Here, since one beacon is transmitted (that is, 1 beacon interval haspassed), the AID reassignment counter value decreases to 29 by 1. Uponreceiving the AID reassignment frame, STA 1 may transmit an ACK frame tothe AP and set the AID reassignment counter value of 29 included in theAID reassignment frame to be an initial value to start the AIDreassignment counter. That is, STA 1 may decrease the AID reassignmentcounter by 1 at beacon intervals (or when the beacon is transmitted).

Then, the AP may transmit a beacon at beacon intervals. STA 2 may wakeup from a power save mode and transmit a PS-Poll to the AP 10. Uponreceiving the PS-Poll from STA 2, the AP may generate the above AIDreassignment frame (new AID: 2000 and AID reassignment counter: 4) andtransmit the generated AID reassignment frame to STA 2. Here, since 26beacons are transmitted (that is, 26 beacon intervals have passed), theAID reassignment counter value decreases to 4 by 26. Upon receiving theAID reassignment frame, STA 2 may transmit an ACK frame to the AP andset the AID reassignment counter value (that is, 4) included in the AIDreassignment frame to be an initial value to start the AID reassignmentcounter. That is, STA 2 may decrease the AID reassignment counter by 1at beacon intervals (or when the beacon is transmitted).

Then the AP may transmit a beacon at beacon intervals, and when fourbeacons are further transmitted (that is, four beacon intervals havepassed), values of the AID reassignment counters for STA 1 and STA 2become zero. When the AP determines the AID reassignment counter, the APmay consider a listen interval of STA 1 and a listen interval of STA 2.Furthermore, STA 1 may change the AID from 1000 to 2000, and STA 2 maychange the AID from 2000 to 1000.

According to an embodiment of the present invention, a collision betweenAIDs may be prevented when an AID of one station is changed or AIDs of aplurality of stations are changed while all of the AIDs are in use.Furthermore, a stable and reliable network service may be provided bypreventing the collision between AIDs, and cost may be saved because anadditional access point does not have to be installed to secure aseparate preliminary AID.

While the example embodiments of the present invention and theiradvantages have been described in detail, it should be understood thatvarious changes, substitutions and alterations may be made hereinwithout departing from the scope of the invention.

What is claimed is:
 1. A method of changing an association ID (AID) of aterminal, the method comprising: receiving a frame including an AIDreassignment element from an access point; determining an AID changetime based on an AID reassignment count value included in the AIDreassignment element; and changing the AID of the terminal to a new AIDdetermined based on AID information included in the AID reassignmentelement at the AID change time, wherein the AID change time isdetermined as a time after beacon intervals corresponding to the AIDreassignment count value have passed since a time at which the frameincluding the AID reassignment element is received.
 2. The method ofclaim 1, wherein, when the AID reassignment count value is zero, the AIDof the terminal is changed to the new AID immediately after receivingthe frame including the AID reassignment element.
 3. The method of claim1, wherein the frame including the AID reassignment element istransmitted by the access point in response to a frame requesting an AIDreassignment transmitted by the terminal to the access point.
 4. Themethod of claim 1, wherein the frame including the AID reassignmentelement is notified to the terminal without a request for the AIDreassignment by the terminal to the access point.
 5. The method of claim1, wherein, when there is at least one another terminal having an AIDthat is to be changed simultaneously with the AID of the terminal, theAID reassignment count value is determined in consideration of both of alisten interval of the terminal and a listen interval of the at leastone another terminal.
 6. The method of claim 5, wherein the AIDreassignment count value has a value such that the AID of the terminalis changed after a longest listen interval among the listen interval ofthe terminal and the listen interval of the at least one anotherterminal.
 7. A method of changing, by an access point, an association ID(AID) of a terminal, the method comprising: generating a frame includingan AID reassignment element, the AID reassignment element including anAID reassignment count value and AID information; and transmitting theframe to the terminal, wherein the AID of the terminal is changed to anew AID determined based on the AID information at an AID change time,the AID change time being determined based on the AID reassignment countvalue, and wherein the AID change time is determined as a time afterbeacon intervals corresponding to the AID reassignment count value havepassed since a time at which the frame including the AID reassignmentelement is received.
 8. The method of claim 7, wherein, when the AIDreassignment count value is zero, the AID of the terminal is changed tothe new AID immediately after receiving the frame including the AIDreassignment element.
 9. The method of claim 7, wherein the frameincluding the AID reassignment element is transmitted by the accesspoint in response to a frame requesting an AID reassignment transmittedby the terminal to the access point.
 10. The method of claim 7, whereinthe frame including the AID reassignment element is notified to theterminal without a request for the AID reassignment by the terminal tothe access point.
 11. The method of claim 7, wherein, when there is atleast one another terminal having an AID that is to be changedsimultaneously with the AID of the terminal, the AID reassignment countvalue is determined in consideration of both of a listen interval of theterminal and a listen interval of the at least one another terminal. 12.The method of claim 11, wherein the AID reassignment count value has avalue such that the AID of the terminal is changed after a longestlisten interval among the listen interval of the terminal and the listeninterval of the at least one another terminal.
 13. A terminal forchanging an association ID (AID), the terminal comprising: atransceiver; and a processor, wherein the processor is configured to:receive, using the transceiver, a frame including an AID reassignmentelement from an access point; determine an AID change time based on anAID reassignment count value included in the AID reassignment element;and change the AID of the terminal to a new AID determined based on anAID information included in the AID reassignment element at the AIDchange time, wherein the AID change time is determined as a time afterbeacon intervals corresponding to the AID reassignment count value havepassed since a time at which the frame including the AID reassignmentelement is received.
 14. An access point for changing an association ID(AID) of a terminal, the access point comprising: a transceiver; and aprocessor, wherein the processor is configured to: generate a frameincluding an AID reassignment element, the AID reassignment elementincluding an AID reassignment count value and AID information; andtransmit, using the transceiver, the frame to the terminal, wherein theAID of the terminal is changed to a new AID determined based on the AIDinformation at an AID change time, the AID change time being determinedbased on the AID reassignment count value, and wherein the AID changetime is determined as a time after beacon intervals corresponding to theAID reassignment count value have passed since a time at which the frameincluding the AID reassignment element is received.